This invention relates to protein food products and more particularly to a method of forming structured protein food products from vegetable and/or animal protein substances.
A highly desirable goal in food processing has been to employ less desirable food materials which are highly nutritious, yet inexpensive, and processing these to result in highly appealing food products. Particular efforts have been directed towards the production of simulated meat products from vegetable and/or animal protein substances. Various degrees of success have been achieved by a variety of processes as is illustrated, for example, by U.S. Pat. No. 2,682,466 to Boyer involving spun filaments and U.S. Pat. Nos. 3,496,858 to Jenkins and 3,940,495 to Flier involving extrusion of vegetable protein materials under conditions of elevated temperature and pressure into a zone of lower pressure to thereby expand the resultant material and produce an expanded textured protein food product which is simulative of a real piece of meat when hydrated.
U.S. Pat. No. 3,920,853 discloses a process for the formation of structured protein food products wherein an aqueous slurry of protein material is frozen into ice crystal layers spaced apart by intermediate layers of slurried protein particles created by formation of the ice crystal layers. Freezing of the slurry causes all of the ice crystal layers to extend in a generally normalized direction to the area or part of the slurry which is contacted with a refrigerating medium. The ice layers cumulatively comprise an in situ matrix which spaces, molds, and compresses the protein layers in striated fashion. Following freezing of the slurry, the next process step is to remove the ice layers and fix the remaining protein layers into a striated arrangement which resembles actual muscle tissue. This is carried out by heating of the frozen slurry at a temperature sufficiently high to fix the protein layers and convert them to a substantially insoluble form while the slurry is in a frozen state. This results in removal of the ice crystal layers and provides protein layers arranged in striated fashion with lines of cleavage generally arranged in the same direction. This novel food product bears a close resemblance to meat as a result of this arrangement of striated protein layers.
The present invention provides a continuous process for the production of a protein food product by the use of an extruder to create a freezing zone to form ice crystal layers of the slurry which cumulatively mold the protein layers in corresponding fashion and provide a protein food product. The unique aspect of this process is achieved by conveyance of the slurry through the extruder with a screw in which the flights of the screw are arranged in helical fashion around the axis thereof. Conveyance of the slurry through the extruder to freeze the same forms an arrangement of helically aligned ice crystal layers in the product which in turn forms the protein material of the slurry into layers in the form of a helix. The resultant structured protein food product having an arrangement of helically aligned protein layers provides the additional advantage of being somewhat tough because the helical arrangement of protein layers permits a cross structuring of the protein layers in a manner such that the toughness of the product is substantially improved. The instant process, furthermore, provides a means of producing a product pursuant to the present invention on a continuous basis.